Multi-element synchronous detection method for regenerated calcium fluoride sludge calcined product

Abstract

The invention relates to the technical field of chemical analysis and detection, and discloses a multi-element synchronous detection method for a regenerated calcium fluoride sludge calcined product, which comprises the following steps: taking a regenerated calcium fluoride sludge calcined product sample, adding an alkaline reagent, an oxidation reagent and a phosphorus-sulfur anchoring agent into the regenerated calcium fluoride sludge calcined product sample, and performing ultrasonic treatment to obtain a sample; performing first-stage heating to obtain a first-stage product; adding an F-complexing agent and an acid digestion reagent into the product in the stage I, and carrying out second-stage heating to obtain a digestion solution; and fixing the volume of the digestion solution, and determining the concentrations of at least two target elements selected from silicon, phosphorus, sulfur, calcium, lead and cadmium in the digestion solution by adopting an inductively coupled plasma emission spectrometer. According to the method, phosphorus and sulfur elements are converted into thermally stable solid-phase salts through a first-stage heating procedure, so that the defect that the recovery rate is low due to the fact that phosphorus and sulfur components are easily volatilized and lost at an acidic high temperature is overcome.

Description

Technical Field

[0001] This invention relates to the field of chemical analysis and detection technology, specifically to a method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge. Background Technology

[0002] In industries such as chemical and metallurgy, a byproduct called regenerated calcium fluoride sludge is often produced. This sludge is typically stabilized or recycled through high-temperature calcination. To ensure the safety and compliance of its subsequent use, precise elemental analysis of the calcination product is essential, particularly monitoring for harmful heavy metals such as lead and cadmium, and assessing the content of key components such as silicon, phosphorus, sulfur, and calcium.

[0003] For elemental analysis of inorganic solids, existing technologies offer a variety of sample pretreatment methods. Conventional acid digestion methods, such as those using nitric acid or aqua regia, are standard methods for treating common inorganic salts and metal oxides, and the process is relatively simple. For samples with high silicon content, technicians also use systems containing hydrofluoric acid, utilizing hydrofluoric acid's unique ability to decompose silicon dioxide. In addition, alkaline melting is a more efficient method, using fluxes such as lithium carbonate and sodium hydroxide to decompose chemically stable materials, such as certain ores and ceramics, at high temperatures.

[0004] However, applying these existing technologies to calcined calcium fluoride sludge at high temperatures encounters a series of problems. First, the calcium fluoride and silica matrix in the calcination products are chemically highly stable, similar to ceramics, and cannot be completely decomposed using only conventional acids such as nitric acid, resulting in the inability to release the encapsulated elements and ultimately leading to low measurement results. Second, if hydrofluoric acid is used to decompose the matrix, the large amount of fluoride ions released will cause strong chemical corrosion to the glass nebulizer and quartz torch of the ICP-OES instrument, severely shortening the instrument's lifespan and affecting data stability. In addition, during the high-temperature strong acid digestion process, phosphorus and sulfur elements in the sample will form volatile acids or gases and be lost, resulting in low recovery rates and unstable results. Finally, if the alkaline melting method is used, although it can decompose the sample, it will introduce a large amount of salt. This high-salt matrix will cause severe signal suppression or physical interference in subsequent ICP-OES detection, making accurate measurement almost impossible. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge, which solves three major technical problems in the processing of such samples: incomplete matrix digestion, severe loss of phosphorus and sulfur elements due to volatilization, and fluoride ion corrosion detection instruments.

[0006] To achieve the above objectives, the present invention provides a method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge, comprising the following steps: S1. Take a sample of the calcined product of the regenerated calcium fluoride sludge, add an alkaline reagent, an oxidizing reagent and a phosphorus-sulfur anchoring agent to the sample of the calcined product of the regenerated calcium fluoride sludge, and perform a first-stage heating to obtain the first-stage product. S2. Add F-complexing agent and acidic digestion reagent to the product of stage one, and perform a second stage of heating to obtain a digestion solution; S3. The digestion solution is brought to a fixed volume, and the concentration of at least two target elements selected from silicon, phosphorus, sulfur, calcium, lead and cadmium in the digestion solution is determined by inductively coupled plasma atomic emission spectrometry.

[0007] By adopting the above technical solution, this invention employs a two-stage heating digestion process to synergistically solve three major problems: element volatilization, matrix interference, and instrument corrosion. Its reaction mechanism is as follows: 1. Phase One (S1): Alkaline oxidation and anchoring, in the first stage of heating, provides an alkaline environment (alkaline reagent) and oxidation conditions (oxidizing reagent) to oxidize the low-valence phosphorus and sulfur components that may be present in the sample to a high-valence state.

[0008] The key lies in phosphorus and sulfur anchoring agents (e.g., those containing Mg). 2+ The addition of reagents allows phosphorus and sulfur elements in the sample to react under alkaline conditions, transforming them into solid salts (such as magnesium phosphate and magnesium sulfate) that are thermally stable and do not easily volatilize in subsequent acidic environments.

[0009] The core purpose of this step (S1) is to fix the volatile P and S elements in the form of non-volatile salts in the solid product, preventing them from escaping in the strong acid and high temperature step of S2, thereby ensuring the recovery rate of P and S elements.

[0010] 2. Phase Two (S2): After the product from stage one has cooled, an F-complexing agent (e.g., boric acid) is added to react with the fluorides (CaF2) in the sample matrix. This reaction removes the highly corrosive F-... - Ions are converted into chemically stable, non-corrosive complexes (e.g., BF4). - This process not only eliminates F - The corrosiveness of the substance also damages the inert matrix structure of CaF2.

[0011] The acidic digestion reagent (e.g., concentrated nitric acid) added subsequently, under the high temperature and high pressure conditions of the second stage heating, is responsible for dissolving the anchoring products (phosphates, sulfates) formed in S1, the metal oxides (PbO, CdO, etc.) in the sample, and decomposing the silicate (SiO2) matrix.

[0012] Due to F - Since it has been complexed, the acid dissolution process of S2 will not generate a large amount of HF, thus avoiding corrosion of the digestion vessel and subsequent ICP-OES injection system (glass nebulizer, torch).

[0013] This invention achieves complete decomposition of the complex matrix of calcined products of regenerated calcium fluoride sludge through solid-phase anchoring in step S1 and complexation defluorination in step S2, while ensuring accurate quantification of elements such as P and S and safe operation of the instrument.

[0014] As a further preferred embodiment of the technical solution of the present invention: Preferably, in step S1, the alkaline reagent is a sodium hydroxide solution; the oxidizing reagent is a hydrogen peroxide solution; and the phosphorus-sulfur anchoring agent is a magnesium nitrate solution.

[0015] Preferably, the concentration of the sodium hydroxide solution is 50%, the concentration of the hydrogen peroxide solution is 30%, and the concentration of the magnesium nitrate solution is 1.0 mol / L.

[0016] Preferably, the first stage of heating in step S1 is microwave heating, with a heating temperature of 100°C to 120°C and a holding time of 10 to 15 minutes.

[0017] By adopting the above technical solution, microwave heating provides rapid, uniform and programmable heating conditions, ensuring that the anchoring reaction of S1 proceeds stably at the set medium and low temperatures (100℃-120℃).

[0018] Preferably, in step S2, the F-complexing agent is a saturated boric acid solution; and the acidic digestion reagent is concentrated nitric acid.

[0019] Preferably, the specific implementation of step S2 includes: (a) cooling the stage one product to room temperature or ice-water bath temperature; (b) adding the saturated boric acid solution to the cooled stage one product; (c) slowly adding the concentrated nitric acid dropwise to the mixture in step (b) while maintaining cooling, so as to control the neutralization reaction rate; and (d) after the concentrated nitric acid has been added, performing the second stage heating.

[0020] By adopting the above technical solution, the S1 product is alkaline, and its neutralization reaction with concentrated nitric acid in S2 will produce a violent exothermic reaction. By (a) cooling, (b) adding a complexing agent buffer first, and (c) adding acid dropwise while maintaining cooling, the rate and temperature of the neutralization reaction can be effectively controlled, preventing sample splashing or digestion vessel leakage due to instantaneous high temperature and pressure, thus ensuring operational safety.

[0021] Preferably, the second stage of heating in step S2 is microwave heating, with a heating temperature of 180°C to 200°C and a holding time of 30 to 45 minutes.

[0022] By adopting the above technical solution, the second stage of heating of S2 requires a high temperature (180℃-200℃) and pressure to ensure that concentrated nitric acid can completely decompose and dissolve the highly inert SiO2 matrix and the anchoring products formed by S1 (such as Mg3(PO4)2).

[0023] Preferably, in step S2, before the second stage heating is performed, a kinetic buffer, which is an aluminum nitrate solution, is added to the stage one product.

[0024] By adopting the above technical solution, Al 3+ Ions can act as kinetic buffers, assisting F-complexing agents (boric acid) in further stabilizing F in the system. - It may also promote the decomposition of SiO2 through complexation, which helps to improve the recovery rate of Si element.

[0025] Preferably, the amount of reagents used in steps S1 and S2, calculated per 0.10 g to 0.25 g of the calcined product sample of the regenerated calcium fluoride sludge, includes: Hydrogen peroxide solution: 3.0 mL to 5.0 mL; Sodium hydroxide solution: 2.0 mL to 3.0 mL; Magnesium nitrate solution: 1.0 mL to 2.0 mL; Saturated boric acid solution: 5.0 mL to 8.0 mL; Concentrated nitric acid: 5.0 mL to 8.0 mL.

[0026] By adopting the above technical solution, the reagent dosage ratio is the result of optimization of this invention, which ensures that within the sample amount range of 0.10g to 0.25g, the added reagent is sufficient to complete the anchoring of S1 and the complexation and acid dissolution of S2, while avoiding excessive redundancy of reagents leading to excessively high total dissolved solids (TDS) in the digestion solution, which would interfere with subsequent ICP-OES determination.

[0027] Preferably, before step S1, a pretreatment step is included for the regenerated calcium fluoride sludge raw material to be tested: the regenerated calcium fluoride sludge raw material is calcined at 850℃±20℃ for 3 hours, and then ground and passed through a 200-mesh sieve to obtain the calcined product sample of the regenerated calcium fluoride sludge.

[0028] By adopting the above technical solution, this pretreatment step ensures that the sample to be tested has a uniform particle size (200 mesh) and stable chemical inertness (calcination at 850℃), which is the basis for obtaining reproducible results in the subsequent digestion step.

[0029] This invention provides a method for simultaneous multi-element detection of calcination products from regenerated calcium fluoride sludge. It has the following beneficial effects: 1. This invention uses an alkaline reagent and an oxidizing reagent in conjunction with a phosphorus and sulfur fixative to treat the sample through a first-stage heating process, converting phosphorus and sulfur elements into thermally stable solid salts. Compared with the strong acid high-temperature digestion scheme used in the prior art, this invention solves the problem that phosphorus and sulfur components are easily volatilized and lost under acidic high temperature, resulting in low recovery rate.

[0030] 2. Before the acid digestion in the second stage, the present invention adds an F-complexing agent (saturated boric acid) to convert the fluorides in the sample matrix into stable non-corrosive complexes. Compared with the existing technology that relies on hydrofluoric acid digestion or does not pretreat the fluorides in the matrix, the present invention effectively avoids the chemical corrosion of subsequent detection instruments by free fluoride ions and extends the service life of the equipment.

[0031] 3. This invention employs a two-stage heating process and strictly controls the acid addition operation in the second stage. By adding a complexing agent first after cooling and then slowly adding concentrated nitric acid, the exothermic neutralization of alkaline products and acidic digestion reagents is effectively controlled, ensuring operational safety. Compared with the one-step strong acid digestion scheme in the prior art, this invention solves the problem of incomplete digestion of highly inert matrices such as calcium fluoride and silicon dioxide, which interferes with subsequent element determination, through the synergistic effect of the two stages. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating the verification of the anchoring effect of P and S elements in a test example of the present invention. Figure 2 This is a schematic diagram comparing the element recovery rates of the test examples and comparative examples of the present invention. Figure 3 This is a schematic diagram comparing matrix effects and interference in the test examples of this invention. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0034] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0035] The calcium fluoride sludge calcination product is derived from a specific industrial fluoride wastewater treatment plant. After being calcined at 800℃±20℃ for 2 hours, the actual sample to be tested is mechanically ground and passed through a 100-mesh (0.150mm) sieve.

[0036] The reagents used to prepare standard simulated sludge calcination products include: high-purity calcium fluoride (CaF2, CAS No.: 7789-75-5); high-purity silica (SiO2, CAS No.: 7631-86-9); high-purity calcium phosphate (Ca3(PO4)2, CAS No.: 7758-87-4); high-purity calcium sulfate (CaSO4, CAS No.: 7778-18-9); high-purity lead oxide (PbO, CAS No.: 1317-36-8); and high-purity cadmium oxide (CdO, CAS No.: 1306-19-0).

[0037] The main process reagents used in this invention include: hydrogen peroxide solution (H2O2, CAS No.: 7722-84-1), an aqueous solution with a mass concentration of 30% (w / w); sodium hydroxide (NaOH, CAS No.: 1310-73-2); magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, CAS No.: 13446-18-9); aluminum nitrate nonahydrate (Al(NO3)3·9H2O, CAS No.: 7784-27-2); and boric acid (H3BO3, CA). S No.: 10043-35-3; Nitric acid (HNO3, CAS No.: 7697-37-2), an aqueous solution with a mass concentration of 68% (w / w); Lithium metaborate (LiBO2, CAS No.: 13453-69-5); Potassium dihydrogen phosphate (KH2PO4, CAS No.: 7778-77-0); Multi-element standard solutions and single-element standard solutions of yttrium (Y) and indium (In), all of which are commercially available national standard substances with a concentration of 1000 mg / L, used for instrument calibration and internal standard testing.

[0038] Deionized water, with a resistivity greater than 18.2 MΩ·cm, is used for the preparation and volume adjustment of all solutions.

[0039] Preparation Example 1: This preparation example provides a standard simulated sludge calcination product (CRM) for method performance testing in subsequent examples and comparative examples. This product has a known chemical composition and chemical inertness. The preparation steps include: 1. Raw material mixing: Accurately weigh 40.0g of high-purity calcium fluoride (CaF2), 40.0g of high-purity silicon dioxide (SiO2), 10.0g of high-purity calcium phosphate (Ca3(PO4)2), 5.0g of high-purity calcium sulfate (CaSO4), 0.10g of high-purity lead oxide (PbO), and 0.10g of high-purity cadmium oxide (CdO) using an analytical balance.

[0040] 2. Ball milling: Place all the above mixed raw materials in a 1L agate ball mill jar, add agate ball milling beads, seal, and dry ball mill on a planetary ball mill at a rate of 300 rpm for 4 hours to ensure that the components are mixed uniformly at both the macroscopic and microscopic levels.

[0041] 3. Calcination: Transfer the ball-milled mixed powder to an alumina crucible and place it in a muffle furnace (programmed temperature furnace). Set the program to heat to 850℃ at a rate of 10℃ / min, and calcine at a constant temperature of 850℃±20℃ for 3 hours to simulate the physical morphology and chemical inertness of actual sludge calcination products.

[0042] 4. Grinding: After the muffle furnace has cooled to room temperature, remove it and transfer the calcined product to a mortar for preliminary grinding. Then, sieve it through a 200-mesh (0.074mm) standard sieve, collect the sieve material, put it into a polyethylene bottle, seal it, and dry it for later use.

[0043] Preparation Example 2: This preparation example provides a chemical anchoring agent for element P used in the embodiments. The preparation steps include: 1. Accurately weigh 25.64g of magnesium nitrate hexahydrate (Mg(NO3)2·6H2O) solid crystals and place them in a 100mL beaker.

[0044] 2. Add about 60mL of deionized water and stir until completely dissolved.

[0045] 3. Transfer the solution to a 100mL volumetric flask, wash the beaker 2-3 times with a small amount of deionized water, and add the washing solution to the volumetric flask.

[0046] 4. Finally, dilute to the mark with deionized water, shake well, and you will get a 1.0 mol / L magnesium nitrate solution. Seal and store for later use.

[0047] Preparation Example 3: This preparation example provides a kinetic buffer for use in the embodiments. The preparation steps include: 1. Accurately weigh 93.78g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O) solid crystals and place them in a 500mL beaker.

[0048] 2. Add about 300mL of deionized water and stir until completely dissolved.

[0049] 3. Transfer the solution to a 500mL volumetric flask, wash the beaker 2-3 times with a small amount of deionized water, and add the washing solution to the volumetric flask.

[0050] 4. Finally, dilute to the mark with deionized water, shake well, and you will get a 0.5 mol / L aluminum nitrate solution. Seal and store for later use.

[0051] Preparation Example 4: This preparation example provides the F-complexing agent used in the embodiments. The preparation steps include: 1. At room temperature (25℃), add 300mL of deionized water to a 500mL beaker.

[0052] 2. Turn on the magnetic stirrer and slowly add boric acid (H3BO3) solid powder to the water. Continue adding and stirring until you observe obvious undissolved boric acid crystals remaining at the bottom of the beaker.

[0053] 3. Stop adding the ingredients, continue stirring for 10 minutes, and then let it stand to settle.

[0054] 4. Take the clear, saturated solution from the upper layer for use. Its concentration at 25°C is approximately 4.5% (w / v). Seal and store for later use.

[0055] Example 1: This embodiment provides a method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge using baseline process parameters. The sample used is the standard simulated sludge calcination product (CRM) prepared in Preparation Example 1, and the method includes the following steps: 1. Accurately weigh 0.1500g of sample and place it in the microwave digestion inner container.

[0056] 2. Stage 1 Reagent addition: Add 4.0 mL of 30% hydrogen peroxide solution, 2.5 mL of 50% sodium hydroxide solution, and 1.5 mL of the P element chemical anchoring agent (1.0 mol / L magnesium nitrate solution) prepared in Example 2 to the container in sequence.

[0057] 3. Microwave Program 1: Tighten the seal on the container and start the microwave program. The temperature will rise to 110℃ within 8 minutes and remain at 110℃ for 15 minutes.

[0058] 4. Cooling: After the process is complete, cool the digestion vessel to room temperature.

[0059] 5. Stage Two Reagent Addition: Carefully open the container. Place the digestion vessel in an ice-water bath for external cooling. Add 6.0 mL of the F-complexing agent (saturated boric acid solution) prepared in Preparation Example 4 and 1.5 mL of the kinetic buffer (0.5 mol / L aluminum nitrate solution) prepared in Preparation Example 3 to the product from Stage One. Then, while maintaining cooling in the ice-water bath and gentle shaking, slowly and dropwise add 7.0 mL of 68% concentrated nitric acid, controlling the neutralization reaction rate, until the concentrated nitric acid is completely added and the reaction becomes relatively stable.

[0060] 6. Microwave Program Two: Tighten the seal on the container again and start the microwave program. Heat to 190℃ within 18 minutes and maintain the temperature at 190℃ for 40 minutes.

[0061] 7. Cooling and Volume Adjustment: After the procedure is complete, cool the digestion vessel to room temperature. After opening the vessel, transfer all the clear solution to a 50mL polypropylene volumetric flask. Rinse the inner vessel and inner cap with deionized water, combine the washings with the flask, and finally adjust the volume to the mark with deionized water. Shake well before testing.

[0062] Example 2: This embodiment provides a method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge using the lower limit of process parameters. The sample used is the standard simulated sludge calcination product (CRM) prepared in Preparation Example 1, to verify the implementation effect under lower process conditions. The method includes the following steps: 1. Accurately weigh 0.2500g of sample and place it in the microwave digestion inner container.

[0063] 2. Stage 1 Reagent addition: Add 3.0 mL of 30% hydrogen peroxide solution, 2.0 mL of 50% sodium hydroxide solution, and 1.0 mL of the chemical anchoring agent for P element (1.0 mol / L magnesium nitrate solution) prepared in Example 2 to the container in sequence.

[0064] 3. Microwave Program 1: Tighten the seal on the container and start the microwave program. The temperature will rise to 100℃ within 5 minutes and remain at 100℃ for 10 minutes.

[0065] 4. Cooling: After the process is complete, cool the digestion vessel to room temperature.

[0066] 5. Stage Two Reagent Addition: Carefully open the container. Place the digestion vessel in an ice-water bath for external cooling. Add 5.0 mL of the F-complexing agent (saturated boric acid solution) prepared in Preparation Example 4 and 1.0 mL of the kinetic buffer (0.5 mol / L aluminum nitrate solution) prepared in Preparation Example 3 to the product from Stage One. Then, while maintaining cooling in the ice-water bath and gentle shaking, slowly and dropwise add 5.0 mL of 68% concentrated nitric acid, controlling the neutralization reaction rate, until the concentrated nitric acid is completely added and the reaction becomes relatively stable.

[0067] 6. Microwave Program Two: Tighten the seal on the container again and start the microwave program. Heat to 180℃ within 15 minutes and maintain the temperature at 180℃ for 30 minutes.

[0068] 7. Cooling and Volume Adjustment: After the procedure is complete, cool the digestion vessel to room temperature. After opening the vessel, transfer all the clear solution to a 50 mL polypropylene volumetric flask, dilute to the mark with deionized water, and shake well before testing.

[0069] Example 3: This embodiment provides a method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge using the upper limit of process parameters. The sample used is the standard simulated sludge calcination product (CRM) prepared in Preparation Example 1, to verify the implementation effect under higher process conditions. The method includes the following steps: 1. Accurately weigh 0.1000g of sample and place it in the microwave digestion inner container.

[0070] 2. Stage 1 Reagent addition: Add 5.0 mL of 30% hydrogen peroxide solution, 3.0 mL of 50% sodium hydroxide solution, and 2.0 mL of the P element chemical anchoring agent (1.0 mol / L magnesium nitrate solution) prepared in Example 2 to the container in sequence.

[0071] 3. Microwave Program 1: Tighten the seal on the container and start the microwave program. The temperature will rise to 120℃ within 10 minutes, and then be maintained at 120℃ for 15 minutes.

[0072] 4. Cooling: After the process is complete, cool the digestion vessel to room temperature.

[0073] 5. Stage Two Reagent Addition: Carefully open the container. Place the digestion vessel in an ice-water bath for external cooling. Add 8.0 mL of the F-complexing agent (saturated boric acid solution) prepared in Preparation Example 4 and 2.0 mL of the kinetic buffer (0.5 mol / L aluminum nitrate solution) prepared in Preparation Example 3 to the product from Stage One. Then, while maintaining cooling in the ice-water bath and gentle shaking, slowly and dropwise add 8.0 mL of 68% concentrated nitric acid, controlling the neutralization reaction rate, until the concentrated nitric acid is completely added and the reaction becomes relatively stable.

[0074] 6. Microwave Program Two: Tighten the seal on the container again and start the microwave program. Heat to 200℃ within 20 minutes and maintain the temperature at 200℃ for 45 minutes.

[0075] 7. Cooling and Volume Adjustment: After the procedure is complete, cool the digestion vessel to room temperature. After opening the vessel, transfer all the clear solution to a 100 mL polypropylene volumetric flask, dilute to the mark with deionized water, and shake well before testing.

[0076] Example 4: This embodiment provides a method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge without the addition of a kinetic buffer (aluminum nitrate solution). The sample used is the standard simulated sludge calcination product (CRM) prepared in Preparation Example 1, which is used to verify the effectiveness of the method when this component is a non-essential component. The method includes the following steps: 1. Accurately weigh 0.1500g of sample and place it in the microwave digestion inner container.

[0077] 2. Stage 1 Reagent addition: Add 4.0 mL of 30% hydrogen peroxide solution, 2.5 mL of 50% sodium hydroxide solution, and 1.5 mL of the P element chemical anchoring agent (1.0 mol / L magnesium nitrate solution) prepared in Example 2 to the container in sequence.

[0078] 3. Microwave Program 1: Tighten the seal on the container and start the microwave program. The temperature will rise to 110℃ within 8 minutes and remain at 110℃ for 15 minutes.

[0079] 4. Cooling: After the process is complete, cool the digestion vessel to room temperature.

[0080] 5. Stage Two Reagent Addition: Carefully open the container. Place the digestion vessel in an ice-water bath for external cooling. Add 7.0 mL of the F-complexing agent (saturated boric acid solution) prepared in Preparation Example 4 to the Stage One product sequentially (without adding the kinetic buffer from Preparation Example 3). Then, while maintaining the ice-water bath cooling and gentle shaking, slowly and dropwise add 7.0 mL of 68% concentrated nitric acid, controlling the neutralization reaction rate, until the concentrated nitric acid is completely added and the reaction becomes relatively stable.

[0081] 6. Microwave Program Two: Tighten the seal on the container again and start the microwave program. Heat to 190℃ within 18 minutes and maintain the temperature at 190℃ for 40 minutes.

[0082] 7. Cooling and Volume Adjustment: After the procedure is complete, cool the digestion vessel to room temperature. After opening the vessel, transfer all the clear solution to a 50 mL polypropylene volumetric flask, dilute to the mark with deionized water, and shake well before testing.

[0083] Comparative Example 1: This comparative example uses the existing hydrofluoric acid-nitric acid digestion method. The specific steps are as follows: Accurately weigh 0.1500 g of sample and place it in a microwave digestion vessel. Add 7.0 mL of 68% concentrated nitric acid and 3.0 mL of 48% hydrofluoric acid (HF). Proceed to 180°C using a microwave program and hold for 30 minutes. After cooling, open the vessel and add 10 mL of the saturated boric acid solution from Preparation Example 4 to complex the residual HF. Reheat to 150°C and hold for 10 minutes. After cooling, bring the volume to 50 mL.

[0084] Comparative Example 2: This comparative example uses the existing strong oxidizing acid digestion method. The specific steps are as follows: Accurately weigh 0.1500 g of sample and place it in the microwave digestion vessel. Add 8.0 mL of aqua regia (3:1 HCl:HNO3) and 2.0 mL of perchloric acid (HClO4). Proceed to 190 °C using a microwave program and maintain the temperature for 40 minutes. After cooling, bring the volume to 50 mL.

[0085] Comparative Example 3: This comparative example uses the existing high-temperature alkaline fusion method. The specific steps are as follows: 0.1500 g of sample is accurately weighed and mixed thoroughly with 1.0 g of spectroscopically pure lithium metaborate (LiBO2) in a platinum crucible. The mixture is placed in a muffle furnace, heated to 950 °C, and melted for 30 minutes. After cooling, the melt is placed in a beaker and dissolved with 40 mL of 5% nitric acid solution under heating and stirring. After cooling, the volume is adjusted to 50 mL.

[0086] Comparative Example 4: Compared to Example 1, the difference is that steps 2 (adding H2O2, NaOH, and Mg(NO3)2 solution), 3 (microwave program I), and 4 (cooling) are not performed. Instead, after placing 0.1500g of sample in the digestion vessel, the process begins directly from step 5 (cooling in an ice-water bath and adding the stage two reagent). All other steps are the same.

[0087] Comparative Example 5: The difference from Example 1 is that, in step 5, the F-complexing agent (saturated boric acid solution) obtained in Preparation Example 4 is not added. All other steps are the same.

[0088] Test Example 1: Objective: To demonstrate the chemical feasibility, instrument safety, and effectiveness of Phase 1 (alkaline anchoring) of this technical solution.

[0089] Experimental steps: 1. To observe the completeness of digestion (appearance), the final volumetric solutions of Examples 1-4, Comparative Example 2 (aqua regia-perchloric acid method), Comparative Example 4 (missing stage one), and Comparative Example 5 (missing F-complexing agent) were taken respectively. Each solution was placed in a 50 mL polypropylene volumetric flask, and under a standard white light source with a white background as a reference, the clarity, color, and presence of any undissolved residue or precipitate of the solution were visually inspected and recorded.

[0090] 2. To conduct instrument safety testing, prepare solution group (a): the test solution prepared according to the complete steps of Example 1; prepare solution group (b): digested according to the steps of Comparative Example 1 (HF-HNO3 method), but omitting the step of adding saturated boric acid solution after final cooling. This solution contains a high concentration of free hydrofluoric acid. Use an ICP-OES equipped with a standard quartz torch and glass nebulizer (Meinhard type). First, continuously pump solution group (b) and run the instrument for 2 hours. After the run, stop the injection and thoroughly clean the injection system with deionized water. Then, remove the quartz torch and nebulizer, and observe the inner wall of the torch center tube and the tip of the nebulizer under an optical microscope, recording any corrosion, scratches, or surface fogging (devitrification). Replace with a brand new quartz torch and nebulizer, and repeat the process, but pump solution group (a).

[0091] 3. To verify the anchoring effect of P and S elements, two 0.1500g portions of Preparation Example 1 (CRM) samples were accurately weighed and designated as Sample A and Sample B, respectively. Using a Grade A pipette, 1.00 mL of potassium dihydrogen phosphate (KH₂PO₄) standard solution (P concentration 1000 mg / L) and 1.00 mL of calcium sulfate (CaSO₄) standard solution (S concentration 1000 mg / L) were added to Sample A and Sample B, respectively. The spiked samples were dried in a 60°C oven to constant weight. Sample A was digested according to the complete procedure of Example 1 (including stage one, alkaline anchoring). Sample B was digested according to the procedure of Comparative Example 4 (missing stage one). Both digests were brought to a final volume of 50 mL, and the concentrations of P and S in the solutions were determined using ICP-OES. Based on the determined concentrations, final volumes, sample weights, and theoretical spiking amounts, the spike recoveries (%) of P and S for Sample A and Sample B were calculated, respectively.

[0092] The experimental data are shown in Table 1: Table 1: Data on feasibility, safety, and anchoring effectiveness of the scheme Conclusion: The data from Test Example 1 verified the feasibility of the technical solution, the safety of the instrument, and the core mechanism.

[0093] Visual observation confirmed the effectiveness of the digestion scheme. The solutions from Examples 1-4 were all clear and transparent, indicating that the two-stage method could achieve complete dissolution of the high-fluorine, high-silicon matrix. The contrast between the milky white turbidity (undissolved CaF2) of Comparative Example 5 (lacking F-complexing agent) and the large amount of residue (undissolved SiO2 / CaSO4) of Comparative Example 2 (aqua regia-perchloric acid method) confirms that the F-complexing agent (saturated boric acid solution) is necessary in this scheme for the synergistic effect of driving CaF2 dissolution and achieving silicon matrix decomposition.

[0094] Instrument safety testing confirmed the instrument compatibility of this method. The solution in Example 1 (with complexed F) did not corrode the standard quartz torch, while the solution in Comparative Example 1 (containing free HF) caused severe nebulization and scoring of the torch. This result indicates that this method, by generating HF in situ and immediately and completely complexing it (generating BF4), is effective. - The strategy of replacing the use of externally toxic hydrofluoric acid (HF) eliminates the risk of corrosion of standard quartz accessories by free HF and improves operational safety.

[0095] Spiked recovery data (Table 1) quantitatively confirm the mechanism of Stage 1 (alkaline anchoring) of this invention. Example 1 (including Stage 1) achieved spiked recoveries of 98.3% and 94.7% for P and S, respectively. Conversely, Comparative Example 4 (lacking Stage 1), using the same Stage 2 high-temperature acid dissolution process, showed recoveries of only 21.4% and 17.8% for P and S, respectively. This data comparison (as shown in Table 1) Figure 1 As shown in the diagram, it is clear that without the alkaline oxidation and anchoring steps of stage one (via H2O2, NaOH, and Mg), 2+ (P and S elements are converted into thermally stable Mg / Ca phosphate and sulfate solid phases). In stage two, P and S elements will be in a high-temperature (180-200℃) strong acid (HNO3) environment as volatile oxides (such as P2O5, SO42-). x The loss of data in the form of [missing information] resulted in a significant underestimation of the analytical results.

[0096] The results of Test Example 1 confirm the two-stage mechanism of this scheme: the alkaline anchoring in Stage 1 is a necessary prerequisite for ensuring accurate quantification of P and S elements; the in-situ acid dissolution-complexation system in Stage 2 is the core to achieve complete dissolution of the high-fluorine silicon matrix and ensure instrument safety.

[0097] Test Example 2: Objective: To quantitatively compare the analytical accuracy of the present invention (Examples 1-4) and comparative examples (Comparative Examples 1-5) for all target elements (Si, P, S, Ca, Pb, Cd) in CRM samples.

[0098] Experimental steps: All test solutions prepared in Examples 1-4 and Comparative Examples 1-5 were used. Multi-element mixed standard solutions containing silicon (Si), phosphorus (P), sulfur (S), calcium (Ca), lead (Pb), and cadmium (Cd) were prepared using inductively coupled plasma optical emission spectrometry (ICP-OES), and calibration curves were established. The concentrations of the target elements in each test solution were determined using standard analytical conditions. The recoveries (%) of each element were calculated based on the theoretical true values ​​from Preparation Example 1 (calculated based on the sample weights and final volumes of each example and comparative example).

[0099] The experimental data are shown in Table 2: Table 2: Comparison of recovery rates (%) of each element in the examples and comparative examples Conclusion: The data from Test Example 2 (Table 2, as shown) Figure 2 (As shown) provides a quantitative evaluation of this scheme and the comparative method.

[0100] Data from Examples 1-3 show that, within the covered process parameters (lower limit, baseline, upper limit), all target elements (Si, P, S, Ca, Pb, Cd) achieved recoveries ranging from 93% to 102%. This indicates that the two-stage method can simultaneously and accurately determine both volatile and non-volatile elements in a high-fluorine silicon matrix.

[0101] The Si recovery (<15%) and Ca recovery (<40%) of Comparative Example 2 (aqua regia-perchloric acid) and Comparative Example 5 (lacking F-complexing agent) were both very low, indicating that the CaF2-SiO2 matrix was undissolved. This result conversely proves the necessity of the F-complexing agent (saturated boric acid solution) in this scheme: the F-complexing agent generated by consuming CaF2 during dissolution... - This drives the dissolution equilibrium to shift in the positive direction and, in conjunction with in-situ HF, achieves the decomposition of SiO2.

[0102] Data from Comparative Example 1 (HF-HNO3) and Comparative Example 4 (missing stage 1) validated the mechanism of stage 1 (alkaline anchoring). While both methods could dissolve the matrix (high Si and Ca recovery rates), the recovery rates of P and S were both below 25%, attributed to the escape of P and S as volatile oxides in the high-temperature, strong acid (stage 2) environment. This contrasts sharply with the high P and S recovery rates (>93%) of Examples 1-3, indicating that the alkaline oxidation pretreatment in stage 1 converts (or anchors) P and S into thermally stable solid phases (phosphate / sulfate), preventing elemental loss in subsequent acid dissolution steps.

[0103] The data from Example 4 (lacking kinetic buffer) (Si recovery 87.3%), compared to Example 1 (Si recovery 98.2%), demonstrate the effect of aluminum nitrate. Aluminum nitrate (Al) 3+ The presence of is not a necessary condition for dissolving Si, but it improves the recovery rate of Si, indicating that it has an optimizing effect on the dissolution process of Si as a kinetic buffer.

[0104] The data from Comparative Example 3 (lithium metaborate melting method) showed good recovery, indicating the effectiveness of the melting method in decomposing insoluble matrices. However, the matrix interference problem of this method will be discussed in Test Example 3.

[0105] Test Example 3: Objective: To compare the degree of matrix interference between the present invention (low-salt system) and Comparative Example 3 (lithium metaborate melting method, high-salt system).

[0106] Experimental steps: 1. Calculate the theoretical total dissolved solids (TDS) concentration (g / L) after making up to 50 mL based on the reagents and sample amount (0.1500 g) used in Example 1. Calculate the theoretical TDS concentration (g / L) after making up to 50 mL based on the flux (1.0 g lithium metaborate) and sample amount (0.1500 g) used in Comparative Example 3.

[0107] 2. To test the matrix inhibition effect, blank solutions for Example 1 (excluding the sample, with all other reagents and steps the same) and Comparative Example 3 (excluding the sample, containing 1.0 g of molten lithium metaborate dissolved in acid, with all other steps the same) were prepared and brought to a final volume of 50 mL. A separate sample of deionized water was used as a reference. 10 μg / L of yttrium (Y) and indium (In) were added to each of the three solutions as internal standards. The three solutions were sequentially introduced into an ICP-OES system, and the signal intensities of Y (371.029 nm) and In (230.606 nm) were recorded. Using the signal intensity in the deionized water reference as 100%, the inhibition rate (%) of the internal standard signal in the blanks of Example 1 and Comparative Example 3 was calculated.

[0108] Experimental data: Table 3: Comparison of matrix effects and interference (TDS vs. signal suppression) Conclusion: The data from Test Example 3 (Table 3) quantifies the matrix effects introduced by different digestion schemes.

[0109] Theoretical calculations show that the TDS of Comparative Example 3 (lithium metaborate melt method) (23.1 g / L) is higher than that of Example 1 (8.4 g / L). The high TDS of Comparative Example 3 mainly comes from the 1.0 g flux (lithium metaborate) required to decompose the sample. This technical solution (Example 1) avoids the use of a large amount of flux through a two-stage wet digestion process.

[0110] Differences in TDS are reflected in matrix suppression effect tests. High TDS (high salt) solutions can cause physical interferences in ICP analysis (such as reduced atomization efficiency and viscosity changes) and plasma loading effects, leading to signal suppression. The blank solution in Comparative Example 3 showed signal suppression rates of 38.4% and 41.2% for yttrium (Y) and indium (In) internal standards, respectively (e.g., Figure 3 (As shown). The blank solution (low TDS) of Example 1 showed signal suppression rates of only 6.8% and 7.5% for the same internal standard.

[0111] The results of Test Example 3 confirm that this technical solution (Example 1) achieves complete dissolution of the high-fluorine silica matrix (see Test Example 2) while obtaining a low TDS test solution. This low matrix effect (low signal suppression) reduces the uncertainty of ICP analysis, reduces reliance on calibration strategies such as complex matrix matching or standard addition methods, and helps improve the accuracy of analytical results.

Claims

1. A method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge, characterized in that, Includes the following steps: S1: Take a sample of the calcined product of the regenerated calcium fluoride sludge, add an alkaline reagent, an oxidizing reagent and a phosphorus-sulfur anchoring agent to the sample of the calcined product of the regenerated calcium fluoride sludge, and perform a first-stage heating to obtain the first-stage product. S2: Add F-complexing agent and acidic digestion reagent to the product of stage one, and perform a second stage of heating to obtain a digestion solution; S3: The digestion solution is brought to a fixed volume, and the concentration of at least two target elements selected from silicon, phosphorus, sulfur, calcium, lead, and cadmium in the digestion solution is determined using an inductively coupled plasma atomic emission spectrometer.

2. The method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge according to claim 1, characterized in that, In step S1: The alkaline reagent is a sodium hydroxide solution; The oxidizing agent is a hydrogen peroxide solution; The phosphorus-sulfur anchoring agent is a magnesium nitrate solution.

3. The method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge according to claim 2, characterized in that, The concentration of the sodium hydroxide solution is 50%, the concentration of the hydrogen peroxide solution is 30%, and the concentration of the magnesium nitrate solution is 1.0 mol / L.

4. The method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge according to claim 1, characterized in that, In step S1, the first stage of heating is microwave heating, with a heating temperature of 100°C to 120°C and a holding time of 10 to 15 minutes.

5. The method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge according to claim 1, characterized in that, In step S2: The F-complexing agent is a saturated boric acid solution; The acidic digestion reagent is concentrated nitric acid.

6. The method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge according to claim 1, characterized in that, The specific implementation methods of step S2 include: (a) Cool the stage one product to room temperature or ice-water bath temperature; (b) The saturated boric acid solution is first added to the cooled product of stage one; (c) While keeping the mixture cooled, add concentrated nitric acid slowly dropwise to the mixture from step (b) to control the rate of neutralization reaction; (d) After the concentrated nitric acid has been added, proceed with the second stage of heating.

7. The method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge according to claim 1, characterized in that, In step S2, the second stage of heating is microwave heating, with a heating temperature of 180°C to 200°C and a holding time of 30 to 45 minutes.

8. The method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge according to claim 1, characterized in that, In step S2, before the second stage of heating, a kinetic buffer, namely aluminum nitrate solution, is added to the product of stage one.

9. The method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge according to claim 1, characterized in that, The amount of reagents used in steps S1 and S2, calculated per 0.10 g to 0.25 g of the calcined product sample of the regenerated calcium fluoride sludge, includes: Hydrogen peroxide solution: 3.0 mL to 5.0 mL; Sodium hydroxide solution: 2.0 mL to 3.0 mL; Magnesium nitrate solution: 1.0 mL to 2.0 mL; Saturated boric acid solution: 5.0 mL to 8.0 mL; Concentrated nitric acid: 5.0 mL to 8.0 mL.

10. The method for simultaneous multi-element detection of calcination products of regenerated calcium fluoride sludge according to claim 1, characterized in that, Before step S1, a pretreatment step is also included for the regenerated calcium fluoride sludge raw material to be tested: the regenerated calcium fluoride sludge raw material is calcined at 850℃±20℃ for 3 hours, and then ground and passed through a 200-mesh sieve to obtain the calcined product sample of the regenerated calcium fluoride sludge.

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